The long term objectives of this work are twofold. First, to develop adaptive machines which can be used effectively in the evaluation and rehabilitation of muscular deficits due to traluma, disuse or disease in a broad spectrum of the population from victims of accidents and chronic musculoskeletal disorders to atheletes and the aged. Second, to collaborate with health professionals in collecting and analyzing data, using the unique capabilities of these devices, and to establish a database to make these data readily accessible. Thus, these machines should be versatile, incorporating active as well as passive exercise capacity, and capable of collecting, archiving, manipulating and comparing quantitative measurements from treatment protocols. The specific aim of this study is to demonstrate the feasibility of developing an intelligent, digital controller, based upon computer architecture widely used and supported in the industrial process control and biomedical communities. The controller must be capable of accurate, on-line, feedback regulation of previously developed instrumented machines. The latter permit motion in three dimensions and employ electrohydraulic control of resistance. To accomplish this specific aim, several steps are required. Initially, the dynamic performance of the electrohydraulic actuator unit must be characterized using standard control engineering test protocols. Next, a prototype test system can be assembled by interfacing a minicomputer with one of the instrumented machines and allowing the computer to emulate digital controller functions. By varying such parameters as sampling rate, data precision and feedback functions, software/hardware constraints will be established. Finally, a configuration will be outlined specifying the requisite hardware and software components which will provide acceptable control performance.